This invention relates to brakes for bending sheet metal such as aluminum siding to be applied to buildings.
Large, stationary brakes for making angular bends in sections of sheet metal which employ a pair of jaws and a bending arm hinged to one of the jaws operative to engage the extending section of a sheet work piece clamped between the jaws have long been used in shops for forming sheet metal duct work and the like. In recent years, the increased use of aluminum as a siding or veneer material for buildings has given rise to the development of a class of portable, lightweight brakes that may be used in the field by workmen applying aluminum siding to a structure. In order to custom form sections required to conform to windows, door openings, etc., these brakes have typically employed a number of spaced C-shaped frame members joined together by rails. A fixed clamping surface extends along one end of the C-shaped frame members and a movable clamping surface is supported on the other edge of the frame which is movable toward and away from fixed surface. U.S. Pat. Nos. 3,559,444, 3,592,037 and 3,817,075 illustrate representative samples of these brakes wherein the movable clamping member is actuated by sliding wedges which move normally to the C-shaped members to force the movable clamp into engagement with the lower clamping member to hold the sheet metal.
In U.S. Pat. No. 3,592,037, a handle disposed at one end of the brake is manually rotatable to actuate the sliding wedges. The pivot point on the handle is coupled to the lower clamping member while the wedges are coupled to the handle a small distance above the pivot point. Unfortunately, with this type of locking mechanism, when the workman reaches the top of the stroke, there is a tendency for him to provide excessive force on the handle. This is due to the fact that unit motion of the handle produces only unit motion of the wedges which, in turn, provides the clamping action between the upper and lower clamping members. Such excessive force has been found to create undue stress on the track on which the wedges are mounted thereby damaging the track and its associated guideways in such manner to cause a loose fit therebetween.
Furthermore, such locking arrangements have prevented the sheet metal from extending beyond the handle since it is coupled to the lower clamping member as well as to the slidable wedges mounted on the upper clamping member. In custom forming sheet metal, it is often desirable to provide a bend only in selected portions of the metal along a transverse cut therein. With the aforementioned locking mechanisms, this cannot be conveniently accomplished since the locking mechanism prevents the portions of the sheet metal which are not desired to be bent from extending beyond the handle.